Tires are sometimes desired having a component comprised of conjugated diene based elastomers and reinforcing filler comprised of precipitated silica. The precipitated silica is often blended with a silica coupler in the rubber composition to couple the precipitated silica to the diene-based elastomers.
An elastomer contained in the rubber composition may be a styrene/butadiene copolymer elastomer.
In one embodiment, the styrene/butadiene elastomer may be a functionalized styrene/butadiene elastomer in a sense of containing at least one functional group (e.g. at least one of siloxy, amine and thiol groups) reactive with hydroxyl groups (e.g. silanol groups) on the precipitated silica to aid in coupling the precipitated silica to the functionalized styrene/butadiene elastomer.
For this invention. it is desired to evaluate providing a functionalized styrene/butadiene elastomer by functionalizing an organic solution polymerization derived styrene/butadiene elastomer (S-SBR) to form a functionalized butadiene/styrene elastomer (Fn-SBR) by reacting the S-SBR in situ within a rubber composition with a minimal amount of mercaptoorganoalkoxysilane (MOAS) to thereby functionalize the styrene/butadiene elastomer within the rubber composition with alkoxysilane functional group of the mercaptoorganoalkoxysilane (MOAS) which is reactive with hydroxyl groups of the precipitated silica reinforcing filler contained in the rubber composition.
For this evaluation, a significant amount of primary silica coupler is also included in the rubber composition in a form of a bis(3-triethoxysilylpropyl) polysulfide (TEOSPS) for coupling diene-based elastomers, including said S-SBR and Fn-SBR in situ within said rubber composition with precipitated silica through hydroxyl groups on said precipitated silica.
For this evaluation, it is contemplated that the mercapto group of the MOAS can readily react with the S-SBR through its vinyl group of its butadiene portion to create Fn-SBR and the silane groups of both the MOAS and the TEOSPS can readily react independently with hydroxyl groups of the precipitated silica. It is contemplated that the polysulfide group of the TEOSPS can subsequently interact in situ with the diene-based elastomers, including the FN-SBR, under conditions of high rubber mixing temperature of the uncured rubber composition and the high curing temperature of the rubber composition.
For this evaluation, to promote a de-coupling of the interaction (e.g. to promote somewhat separated reactions) of the mercapto group of the MOAS with the S-SBR to form the FN-SBR, reaction of the silane groups of the MOAS, Fn-SBR and TEOSPS with the hydroxyl groups of the precipitated silica and interaction of the polysulfide of the TEOSPS with the diene-based elastomers in the rubber composition, only a minimal amount of the MOAS is used and a significant amount of the TEOSPS is employed in the rubber composition. For example, a ratio of the TEOSPS to MOAS in a range of from about 3/1 to about 30/1, alternatively 5/1 to 20/1, might be used.
For the preparation of the rubber composition, a mixing procedure is comprised of at least one preliminary mixing step, or stage, usually sequential mixing steps (one mixing step followed by a next mixing step), which are sometimes referred to as non-productive mixing steps. Such non-productive mixing steps do not contain sulfur curatives in a form of sulfur and sulfur vulcanization accelerators. Following the non-productive mixing step(s), a final mixing step is provided in which sulfur and sulfur vulcanization accelerator(s) are added to the rubber composition. Such final mixing step is referred to as a productive mixing step. In such productive mixing step, sometimes additional rubber ingredients are also added to the rubber composition as may be desired. Such preparation of rubber compositions by the aforesaid non-productive (NP) and productive (P) mixing steps is well known by those having skill in the rubber compounding art.
In the description of this invention, the terms “compounded” rubber compositions and “compounds” are used to refer to rubber compositions which have been compounded, or blended, with appropriate rubber compounding ingredients. The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The amounts of materials are usually expressed in parts of material per 100 parts of rubber by weight (phr).